Continuous crystallizer



l.lume 16,` 1931.

w. H. LoHMANN- CONTINUOUS CRYSTALLIZIH Filed Feb. 5. 1927 n y INVENTOR Ma.. lf. LAW

,I BY E A ATTORNE` Patented June 16, 1931 UNITED vSTATES PATENT OFFICE WILLIAM H. LOHMANN, OF WILMINGTON, DELAWARE, ASSIGNOR T GENERAL CHEMI- CAL COMPANY, 0F NEW YORK, N. Y., A CORPORATION OIF NEW YORK CONTINUOUS CRYSTALLIZER` Application led February 5, 1927. Serial No. 166,035.

This invention relates to improvements in continuous crystallizers of the type utilizing a helical ribbon conveyor to prevent adherence of crystals to the cooling surfaces as well as to carry the mixture of crystals andfmother liquor through the crystallizer.

An object of this invention is to improve the discharge of crystals from a crystallizer of the helical conveyor type to obtain a product of more uniform size than is possible with known crystallizers of this type and to prevent the accumulation of large crystals in the crystallizing chamber. A further object of the invention is to provide a means of discharge which will attain these results and yet be simple and cheap of construction, durable, require a minimum of attention, and be of such nature that it may be easily applied to existing forms of apparatus.

l `Referring to the accompanying drawings illustrating an embodiment of my invention, Fig. 1 is a perspective view of a continuous crystallizer with the end and top plates removed, to which my invention has been applied Fig. 2is a sectional view substantially on the line 2-2 of Fig. 3; Fig. 3 is an end elevation showing the relative position of the discharge opening to the discharge end of the conveyor trough; and Fig. .tis a sectional view substantially on the line 4 4 of Fig. 2. The crystallizer consists essentially of a cast or sheet metal shell 5 to which end plates 6 and 7 and atop plateS are fastened to form the crystallizing elongated chamber 9. The lower part of the shell is semicircular in cross section and is surrounded Vby a" jacket 10 through which Hows a cooling medium such as water, generally in counter current flow to the solution to be crystallized. The inlet 40 and discharge ports for the cooling medium are not shown but can be arranged in any conventional manner. f

The end plates 6 and 7 have journaled therein at 11 the shaft 12 which is continuously driven during the operation of the crystallizer by some means such as the gear 13.

Arms 14: are fastened at intervals to the shaft 12 to support the ribbon conveyor and Y scraper 15. The ribbon is helically arranged in the chamber 9 and has .a comparatively long pitch. The face of the ribbon is at every point radial to the shaft. One or more of the ribbons 15 can be fastened to the shaft 12 as desired; in actual practice three ribbons are usually used. The assemblage of shaft 12, arms 14 and ribbons 15 constitutes a helical conveyor which serves the triple purpose of causing agitation of the liquor, conveyingl the crystals which have formed through the crystallizer, and preventing the adherence of crystals to the bottom and sides of the chamber. Upon rotation the ribbons traverse a path conforming to the contour of the bottom of the chamber and thus act as Scrapers to prevent the adherence of crystals to the bottom of the chamber and as con-` veyors to move the crystals lengthwise through the chamber.

The hot saturated solution to be crystal-k lized is fed to the chamber 9 through an inlet port 16 located, as shown in Fig. 2, at the upper 'left hand end of the shell. The mother liquor and crystals are discharged through a port 17 in the end plate 6. The exact location of the inlet port is immaterial but the exact location of the discharge port in the end plate 6 is important.

At the discharge end of the chamber the ribbon 15 has fastened thereto or made integral therewith a scoop 18. This scoop, which extends back along the ribbon only a short distance, may be formed by attaching a strip of sheet metal to the inner edge of the ribbon at right angles to the face of vthe ribbon and projecting therefrom in the direction of rotation'thereof, or by attaching a length of angle iron to the.' face of the ribbon, or in any other suitable manner. vWhen the interior end of the scoop is elevated, the scoop acts as a trough down which the mother liquor and crystals flow due to the pitch of the ribbon. The previously described discharge port 17 is located at the liquid level in the end member 6 in such a position that it will register with the discharge end of the trough formed by the scoop 18 when the other end of the trough is at or very near the top of the i This is clearly shown in Figs. 2

eral decks forming separate cham ers at varying heights so that the solution will flow byl gravity from one chamber to the next, or may be arranged to form one long continuous chamber. It has been found in practice that when using three decks it is generally necessary to add the scoops only to the lower two as there is not enough crystallization in the upper deck or chamber to warrant the use of a scoop.

The operation is as follows:

The hot saturated solution is fed to the receiving end of the crystallizin chamber with a constant, uniform flow an a cooling medium is passed constantly through the jacket in counter current flow to the solution. As the liquor comes into contact with the cooled surface of the chamber crystals are formed. These crystals, which become larger as they move along, are conveyed the total length of the crystallizing chamber by means of the helical `conveyor. The conveyor acts at the same time as an agitator to keep the solution thoroughly stirred and also as a means of scra ing the crystals from the bottom of the chamber as they are formed.

While the crystals are small they remain in suspension for a comparatively long period, but upon becoming larger they tend to settle out more rapidly. At the discharge end of the chamber the crystals are so large that there is a tendency for them to slide off the ribbon and fallback to the bottom of the chamber as soon as the face of the ribbon is hi her than the axis of the shaft.

en dischar ing the crystals in the customary manner y' causing the liquor containin crystals in suspension to overow throug an orifice in the wall of the chamber at the liquid level, the discharged liquor contains a smaller pro ortion of crystals than if all of the crys s remained in suspension. The crystals which settle out of suspension and remain behind tend to grow larger, until iinally the entire contents of the crystallizer must be cleaned outmanuall My construction overcomes these diities by providing for the removal of a comtplosite mass of crystals from the bottom of e chamber immediately adjacent the discharge end. The trough formed by the scoop retains a mass of crystals along with some of the mother liquor. The entrapped liquor flows down the trough, due to the pitch of the ribbon, and washes the crystals out the discharge port.

The continuous 'removal of a composite mass of crystals from the. bottom of the chamber prevents the accumulation of large crystals and thus ermits continuous, uniform operation. anual control is reduced to a minimum, and in addition the construc- 'tion which I have devised may be easil applied to existing forms of apparatus wit but ittle modification.

I claim:

1. A continuous crystallizer com rising a crystallizing chamber, inlet and ischarge ports for said chamber, a helical conveyor rotatable in said chamber, and means cooperating with said helical conveyor for scooping up the crystals formed in said chamber and for conveying the crystals to the discharge port.

2. A continuous crystallizer com rising a crystallizing chamber, inlet and ischarge ports for said chamber, a helical conveyor rotatable in said chamber, and a scoop attached to and forming a part of the discharge end of said helical conveyor for retaining a composite mass of the crystals formed in said chamber and for conveying the crystals to the discharge port.

3. A continuous crystallizer comprising a crystallizing chamber, a plurality of helical shaped members rotatably arranged in said chamber for conveying the crystals to its discharge end, means on said rotatable helical shaped members forming scoops during part of their rotation and forming troughs during another part of their rotation, an inlet port for said chamber, and a discharge port for said chamber arranged to register with said means when the troughs are formed whereby crystals scooped up by said means are discharged from said chamber.

4. A continuous 4crystallizer as claimed in claim 3 in which the crystallizing chamber is defined by a casing having end members and the discharge port is located in one of said end members.

5. A continuous crystallizer com rising a crystallizing chamber, inlet and ischarge ports for said chamber, a helical ribbon conveyor rotatable in said chamber, and a scoop attached to said ribbon adjacent the discharge end for retaining a composite mass of the crystals formed in said chamber and for conve ing the crystals to the discharge port- 6. n a continuous crystallizer havin an elon ated crystallizing chamber with inlet and ischarge orts, means for conveying the crystals forme in said chamber to the discharge end of said chamber and means directly associated with the conveying means for forming a trough attached to said conveying means for scooping up the crystals and discharging them through the discharge port.

7. A continuous crystallizer comprising a crystallizing chamber adapted to contain a bod of li uor, inlet and dischar e ports for sai cham r, a conveyor rotata le in said chamber adapted to agitate said liquor and cause movement of crystals toward the discharge end of said chamber, and a scoop actuated by said conveyor and caused to rotate 'nsl therewith, said scoop beingishaped to form a trough adapted to contain a mass of c stals during its upward travel through the liquor, said trough having its discharge end in registry with said discharge port and its opposite end above the level of said discharge port at its point of emergence from said liquor, whereby the contained crystals will flow downwardly through said trough and out said f discharge port.

8. A continuous crystallizer comprising a e crystallizing chamber having a bottom of substantially semicircular cross section, inlet and discharge ports for' said chamber,l a shaft rotatable in said chamber, a plurality of helical members supported by said shaftand having faces radial to said shaft arranged upon rotation to traverse a path conforming to the contour of the bottom of the chamber, and means on said members projecting therefrom in the direction of rotation thereof and forming a trough therewith, said discharge port being located to registervwith the ends of said troughs during rotat'in' of". said members V whereby the crystals at the discharge end of Y said chamber are scooped up and discharged a troug out said discharge port.

9. A continuous c stallizer comprising an elongated crystallizing chamber provided with inlet and discharge ports and adapted to contain a body of liquor, said discharge port being located at the li uid level in one end of said chamber, means or conveying the crystals formed in said chamber lengthwise' therethrough to the end thereof in which said discharlge port is located, and means forming attached to said conveying means for scooping up the crystals and discharging them through the dischar ve port.

10. A continuous' crysta lizer com rising a crystallizing chamber, inlet and ischarge ports forsaid chamber, a helical ribbon conveyor rotatable in said chamber, and a member associated with said ribbon adjacent the discharge end of the crystallizer for forming with said ribbon a scoop for conveying crystals yto the discharge ort.

I n testimony whereof, aiix my signature.

- WILLIAM H. LOHMANN. i 

